1. Field of the Invention
This invention relates to apparatus for obtaining samples of flowing fluid streams substantially identical in composition to the composition of the flowing streams.
2. Description of the Prior Art
In sampling flowing oil wells, reliable and accurate means of sampling is urgently needed to determine sand concentrations so that appropriate sand control techniques can be implemented when needed. Significant sand production is occurring in the newly developing areas of crude oil production. A means of sampling produced fluids to determine accurately and efficiently the amount of sand produced is currently unavailable. To compound the sampling problem, many oil wells are being produced at extremely high rates, i.e., 5,000 to 30,000 barrels (795 to 4,770 cubic meters) of oil per day. This complicates the technique of capturing representative samples of the flowing stream because it would be impractical to divert entire high velocity streams for short enough periods of time to obtain manageable size samples.
Securing true samples of sand entrained in a flowing fluid can be difficult. One problem is that any change in the kinematic conditions of the system will cause heavier and lighter particles in the fluid to flow along different paths depending on the pressure changes occuring along the different paths. Placing a sampling device in the flow stream is enough in itself to produce changes in the kinematic conditions of the system so that it becomes difficult or impossible to obtain a true and accurate sample of the material moving along the flow stream.
Another problem in obtaining representative samples of a well fluid containing solids is that stratification or irregular dispersal of the solid particles may occur in the kinematic system, hence a sample of only a portion of the stream may not necessarily be representative of the composition of the flow.
The inadequacy of sampling a flowing stream, particularly containing entrained solids such as sand, with a non-isokinetic sampling system has been recognized and attempts have been made to devise isokinetic systems; see for example, U.S. Pat. Nos. 3,473,388 issued Oct. 21, 1969 and 3,921,458 issued Nov. 25, 1975. A principal disadvantage with these isokinetic sampling devices is that outside pumping and instrumentation are necessary to establish isokinetic sampling.
A need exists for an improved apparatus and method for isokinetic sampling of flowing dispersions.